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esm: avoid import.meta setup costs for unused properties #57003

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esm: avoid import.meta setup costs for unused properties #57003

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b3575a0
esm: avoid `import.meta` setup costs for unused properties
JakobJingleheimer Feb 11, 2025
07597a5
!fixup: correct autocomplete of prop name
JakobJingleheimer Feb 11, 2025
c3c12a4
fixup!: add test case for re-assigning `dirname` & `filename`
JakobJingleheimer Apr 22, 2025
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esm: avoid import.meta setup costs for unused properties
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@JakobJingleheimer
JakobJingleheimer committed Feb 11, 2025
commit b3575a09b6323a2edf6091f43a9f50c091956940
26 changes: 23 additions & 3 deletions lib/internal/modules/esm/initialize_import_meta.js
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Original file line number Diff line number Diff line change
@@ -1,6 +1,8 @@
'use strict';

const {
ObjectDefineProperties,
ObjectDefineProperty,
StringPrototypeStartsWith,
} = primordials;

Expand Down Expand Up @@ -60,9 +62,27 @@ function initializeImportMeta(meta, context, loader) {
if (StringPrototypeStartsWith(url, 'file:') === true) {
// These only make sense for locally loaded modules,
// i.e. network modules are not supported.
const filePath = fileURLToPath(url);
meta.dirname = dirname(filePath);
meta.filename = filePath;

// Avoid paying the cost to derive these unless they're actually accessed.
ObjectDefineProperties(meta, {
dirname: {
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get() {
const value = dirname(this.filename);
ObjectDefineProperty(this, 'dirname', { __proto__: null, value });
return value;
},
__proto__: null,
},
filePath: {
get() {
const value = fileURLToPath(url);
ObjectDefineProperty(this, 'filename', { __proto__: null, value });
return value;
},
__proto__: null,
},
__proto__: null,
});
}

if (!loader || loader.allowImportMetaResolve) {
Expand Down